The present invention relates to energetic materials, also referred to as reactive materials, particularly to improvements in the energy release rate, energy density, mechanical properties, processability, and related properties thereof by substituting substantially amorphous metal alloys for the conventionally used crystalline metal alloys.
Energetic materials, also called reactive materials, are those that release significant amounts of energy in response to an external stimulus, through chemical reactions taking place within the material and/or between the material and its environment. Examples of energetic materials include fuels, propellants, pyrotechnics, and explosives.
The chemical reactions commonly associated with energetic materials include combustion, pyrolysis, thermite, and intermetallic synthesis reactions, as well as combinations thereof. Depending on the application, energetic materials are chosen to respond to trigger stimuli (e.g. electrical signals, heating, vibration, shock, or impact) by emitting energy in the form of light, heat, pressure, etc.
Among the most common chemical reaction used in energetic materials is the thermite reaction, defined as the transfer of oxygen or halogen atoms from an oxidizer phase to a fuel phase. Commonly used oxidizers include metal oxides like Fe2O3, MoO3, MnO2, WO3, or CuO, oxidizing salts like permanganates, perchlorates, or carbonates, and fluoropolymers like polytetrafluoroethylene (PTFE or Teflon®) or polyvinylidene difluoride (PVDF). Commonly used fuels include active metals like Al, Mg, Ti, or Zr. The ratio of oxidizer to fuel, often called the equivalence ratio, may vary widely depending on the reactants used and the desired properties. See for instance U.S. Pat. Nos. 5,886,293 and 6,593,410.
Thermites can be used in loose powder form, where the fuel and oxidizer are synthesized as powders and mechanically blended, or as energetic composites, in which the loose powders have been compacted into a load-bearing solid using a combination of heat and mechanical forces. Forming energetic composites can improve volumetric energy density and enable new applications, such as the substitution of thermite composites for inert structural materials in certain munitions. See, for instance, published U.S. Pat. App. No. US 2007/0277914.
In many applications, energetic materials are sought that emit the largest amount of energy in the shortest amount of time. The advent of nanotechnology has enabled finely-controlled energetic material systems wherein the rate-controlling mass transport steps in energy release can be dramatically accelerated by reducing reactant sizes to the nanoscale, promoting more intimate nanoscale mixing, increasing the surface area available for the reaction to occur, and lowering the melting point of the fuel to help the reaction begin earlier during ignition. These so-called nanoenergetic materials have enabled revolutionary improvements in reaction efficiencies, energy release rates, and other useful properties. Nanoenergetic materials based on thermite reactions are often called nanothermites or metastable intermolecular composites (MIC). See, for instance, U.S. Pat. No. 5,266,132.
Nanothermites/MIC have certain drawbacks, however. Notably, high surface areas for ultra-fine fuel and oxidizer phases lead to high reactivity with environmental air, water, and other contaminants, and increased sensitivity to electrostatic discharge (ESD). Fine powders are also greater inhalation hazards, and are more difficult to disperse uniformly and consolidate into dense, strong composites. Methods for achieving high energy release rate without incurring the above performance and composites processing penalties of nanothermites/MIC would be of great value to the art.
Amorphous materials are not entirely unknown in the prior art of energetic materials; however, the amorphous materials employed in the present invention and their use are completely different from prior amorphous materials. For instance, U.S. Pat. No. 5,625,165 teaches the use of amorphous azide, cyclic nitramine, or ozone primary high explosives for reduced sensitivity to mechanical and thermal shock. Those disclosed materials are nitrogen- or oxygen-based molecular explosives and not metal alloys, so their properties are quite different. For instance, amorphous characteristics in those disclosed materials were being investigated to reduce ignition sensitivity to mechanical loading not, as in the present invention, for increased ignition sensitivity which is completely opposite.
U.S. Pat. No. 4,632,714 teaches the use of amorphous salts, not amorphous metals. In particular, amorphous ammonium, alkali, and alkaline earth salts are used as oxidizers, not as fuels. There was no recognition that using nitrogen based amorphous salts as oxidizers also provided the benefits of amorphous metal alloys as fuels. Furthermore the benefits derived from using amorphous metals as fuels in explosives are far different when compared to the benefits of using amorphous salts as oxidizers in explosives.
U.S. Pat. No. 5,547,525 teaches the use of amorphous carbon as an additive to increase electrical conductivity in energetic materials and thereby reduce electrostatic discharge sensitivity; in this case the materials are again distinct from those used in the present invention hereinafter described, and the amorphous carbon was neither a fuel nor an oxidizer, nor even a reactant in the energetic system.
In energetic and nanoenergetic/MIC materials known in the art, the fuel comprises a crystalline metal. The present invention, however, relates to energetic or nanoenergetic materials wherein the fuel comprises a substantially amorphous metal.
The present invention uses amorphous metals as fuels in an energetic mixture or composite and is based on my recognition that the use of the amorphous metal fuels improves the processability, mechanical properties, and energy release characteristics of energetic compositions while also making the resulting amorphous composite energetic composite a usable structural material with safe but usable practical energetic properties.
Other objectives and benefits of the present invention will become apparent to those skilled in the art from the subsequent description, wherein are shown and described the modes currently deemed best suited to carry out the invention. As will become apparent to those skilled in the art, my invention is capable of various other embodiments, which do not depart from the key features of my invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive.